Optical film

ABSTRACT

The invention provides a light emitting apparatus including a projector color wheel and a light emitting diode (LED) device using a composite material, a method of manufacturing the composite material, and an optical film. The stability of the composite material has been greatly improved. Light emitting devices using the composite material have wide color gamut.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the prioritybenefit of U.S. application Ser. No. 15/490,766, filed on Apr. 18, 2017,now pending. The entirety of the above-mentioned patent application ishereby incorporated by reference herein and made a part ofspecification.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to an optical film using acomposite material.

2. Description of Related Art

Projector is a display device used for producing large size images. Aprojector is to convert an illumination beam produced by a light sourcemodule into an image beam by using a light valve, and project the imagebeam onto a screen or a wall through a projection lens to form an image.

In order to produce illumination beams of three primary colors (red,blue, green), some projectors are configured with color wheels. Theprojector color wheel has a plurality of light converting regions (forexample, filter regions or phosphor regions). The light convertingregions are able to convert, for example, an incident beam produced bythe light source into the required color beam.

When in operation, the projector color wheel is exposed to hightemperature (up to 180° C.) and intensive light within the projector.Similarly, the surface temperature of a light emitting diode (LED) chipcan be up to 120° C., with intensive illumination of light emitted fromthe LED chip. Currently, phosphors are used in combination with a bluelight source to produce a white light. In order to improve the colorgamut, it is desirable to use quantum dots (QDs) instead of theconventional phosphors. However, the high temperature and the intensivelight will damage the QDs very quickly. In the situation, the luminanceof the QDs will be lost permanently.

SUMMARY OF THE INVENTION

The invention provides an optical film using a composite material. Thecomposite material includes a plurality of quantum dots and a silicamaterial encapsulating surfaces of the quantum dots. Therefore, thethermal stability is enhanced by using silica (SiO₂) material toencapsulate the quantum dots.

In an embodiment of the invention, an optical film includes a firstcomponent, a second component, and a third component. The firstcomponent includes a plurality of quantum dots and a silica materialencapsulating surfaces of the quantum dots. The second componentincludes a UV curable composite material. The first component isdispersed in the second component. The third component includes two PET(polyethylene terephthalate) substrate sheets. The first component andthe second component are disposed between the two PET substrate sheets.

In an embodiment of the invention, the silica material includes aninorganic polymer made from tetramethyl orthosilicate (TMOS) ortetraethyl orthosilicate (TEOS).

In an embodiment of the invention, the UV curable composite materialincludes 2-phenylethyl methacrylate, triaryl isocyanurate (TAIC),diallyl phthalate, and a photoinitiator.

In an embodiment of the invention, the optical film is used in a lightemitting apparatus, such as a backlight unit in a flat-panel displayapparatus, a liquid crystal display monitor or other similar visualdisplay apparatus.

Based on the above, the invention provides an optical film using acomposite material. The optical film includes a first component, asecond component and a third component. The first component includes thecomposite material having a plurality of quantum dots encapsulated by asilica material. The first component is dispersed in the secondcomponent including a UV curable composite material. The first componentand the second component are disposed between the third componentincluding two PET substrate sheets. The thermal stability of thecomposite material is enhanced by using the silica material toencapsulate the quantum dots. Moreover, the quantum dots are uniformlydispersed in the silica material (e.g., encapsulating material). As aresult, the luminescence efficacy of the composite material is improvedwhich is suitable for a backlight unit, projector color wheels andsurface packaging of photoelectric devices, such as LED devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a front view illustrating a projector color wheel according toa first embodiment of the invention.

FIG. 2A is a schematic drawing illustrating a composite materialaccording to a second embodiment of the invention.

FIG. 2B is a schematic drawing illustrating a composite materialaccording to a third embodiment of the invention.

FIG. 3 is a flow-chart drawing illustrating a manufacturing flow of acomposite material according to a fourth embodiment of the invention.

FIG. 4A and FIG. 4B are schematic drawings illustrating themanufacturing flow of the composite material according to FIG. 3.

FIG. 5 is a transmission electron microscopy (TEM) image of a compositematerial of Experimental example 1.

FIG. 6A is a green test screen from DLP projector of Experimentalexample 2.

FIG. 6B is a red test screen from DLP projector of Experimental example3.

FIG. 7 is a LED output spectrum of Experimental example 4.

FIG. 8 is a LED output spectrum of Experimental example 8.

FIG. 9 is a luminescence intensity of Experimental example 9.

FIG. 10 is a plot of LED efficacy of Experimental example 5 andComparative example 1.

FIG. 11 is a schematic drawing illustrating an optical film according toan embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the invention is illustrated more comprehensively referringto the drawings. However, the invention may be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Thicknesses of layers and regions in thedrawings may be enlarged for clarity. The same or similar referencenumbers represent the same or similar components, and are not repeatedagain in the following paragraphs.

In the present specification, ranges represented by “a numerical valueto another numerical value” are schematic representations to avoidlisting all of the numerical values in the range in the specification.Therefore, the recitation of a specific numerical range discloses anynumerical value in the numerical range and a smaller numerical rangedefined by any numerical value in the numerical range, as is the casewith any numerical value and a smaller numerical range stated expresslyin the specification. For instance, the range of “a size of 100 nm to500 nm” discloses the range of “a size of 200 nm to 350 nm”, regardlessof whether other numerical values are listed in the specification.

FIG. 1 is a front view illustrating a projector color wheel according toa first embodiment of the invention.

Referring to FIG. 1, the projector color wheel 10 of the firstembodiment includes a plurality of different color converter regions 12,14 and 16 and a rotating portion 18. The color converters 12, 14 and 16are arranged to form a disk configuration. The rotating portion 18 isdisposed at a center of the disk configuration. That is, the colorconverters 12, 14 and 16 are arranged as an annular shape whichsurrounds a circumference of the rotating portion 18. Rotation of therotating portion 18 may drive the projector color wheel 10 to rotate.Specifically, by controlling rotation of the projector color wheel 10according to the time sequence, an illumination beam from a light sourcedevice (not shown) is converted or filtered into various light beams ofdifferent colors according to the time sequence when passing through thedifferent color converter regions of the projector color wheel 10.

In some embodiments, the illumination beam from a light source devicemay be blue illumination beam. The converter regions would separatelyconvert blue illumination beam to green and red beams. In alternativeembodiments, illumination beam from a light source device may be shortvisible (e.g., a wavelength thereof is about 405 nm) or ultraviolet (UV)illumination beam. The converter regions would separately convert Vis orUV illumination beam to blue, green, and red beams.

In some embodiments, the color converter 12 may be an opening, atransparent region without color for letting the illumination beam (forexample, a blue illumination beam) to pass through directly withoutaltering color. In alternative embodiments, the color converter 12 maybe a reflective surface for letting the illumination beam (for example,a blue illumination beam) to reflect without altering color. The colorconverters 14 and 16 may include different composite materials, whichare called as a first color converter 14 and a second color converter 16hereinafter. The first color converter 14 may include a first compositematerial for converting the illumination beam into a first colorillumination beam (i.e., to change a wavelength of the illuminationbeam). On the other hand, the second color converter 16 may include asecond composite material for converting the illumination beam into asecond color illumination beam. In one embodiment, the first colorillumination beam differs from the second color illumination beam.Namely, a wavelength of the first color illumination beam differs from awavelength of the second color illumination beam. For example, the firstcolor converter 14 may convert the illumination beam into red beam,while the second color converter 16 may convert the illumination beaminto green beam. However, the invention is not limited thereto. Inanother embodiment, the composite materials may be chosen according tothe needs of color. In alternative embodiment, a particle size andcomposition of a quantum dot of the first composite material differsfrom a particle size and composition of a quantum dot of the secondcomposite material. Although only three color converters are illustratedin FIG. 1, but the invention is not limited thereto. In otherembodiments, a number of the color converters and the color of theconverters may be adjusted according to the design.

FIG. 2A is a schematic drawing illustrating a composite materialaccording to a second embodiment of the invention. FIG. 2B is aschematic drawing illustrating a composite material according to a thirdembodiment of the invention.

Referring to FIG. 2A and FIG. 2B, each of the foregoing compositematerials includes at least one quantum dot and a silica material. Indetail, as shown in FIG. 2A, one quantum dot 102 a is located in asilica material 104 a to form a composite material 100 a. That is, asurface of the one quantum dot 102 a is encapsulated by the silicamaterial 104 a. Similarly, as shown in FIG. 2B, a plurality of quantumdots 102 b are dispersed uniformly in a silica material 104 b to form acomposite material 100 b. Surfaces of the quantum dots 102 b areencapsulated by the silica material 104 b. Although only four quantumdots 102 b are illustrated in FIG. 2B, but the invention is not limitedthereto. In other embodiments, a number of the quantum dots may beadjusted according to the design.

In one embodiment, a particle size W1 of the composite material 100 a isless than a particle size W2 of the composite material 100 b. Theparticle size W1 of the composite material 100 a and the particle sizeW2 of the composite material 100 b may respectively range from 10 nm to500 μm. In another embodiment, the particle size W1 of the compositematerial 100 a and the particle size W2 of the composite material 100 bmay respectively range from 10 nm to 1 μm.

In some embodiments, the quantum dots 102 a and 102 b refer tonanostructures that are substantially monocrystalline. However, theinvention is not limited thereto. In other embodiment, the quantum dots102 a and 102 b refer to nanostructures that are polycrystalline oramorphous.

In some embodiments, the quantum dots 102 a and 102 b may be corestructure, core-shell structure, core-multishell structure, alloystructure, core-alloy layer-shell structure, core-alloy layer-multishellstructure, core-gradient alloy-shell structure, or a combinationthereof. When the quantum dots 102 a and 102 b are core-shell structure,each of the quantum dots 102 a and 102 b includes a core structure and ashell structure covering the core structure. The core structure may beselected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe,HgS, HgSe, HgTe, GaN, GaP, GaAs, InP, InAs, InSb, AlN, AlP, AlAs, AlSb,SiC, Fe, Pt, Ni, Co, Al, Ag, Au, Cu, FePt, Si, Ge, PbS, PbSe, PbTe, andalloys thereof. The shell structure may be selected from the groupconsisting of ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, AlN,AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, GaSe, InN, InP, InAs, InSb, TlN,TlP, TlAs, TlSb, PbS, PbSe and PbTe, and alloys thereof. However, theinvention is not limited thereto. In other embodiment, the quantum dots102 a and 102 b may be perovskite.

In some embodiments, the silica materials 104 a and 104 b may be anetwork of alternating crosslinked silicon (Si) and oxygen (O) extendingin all possible directions, which may be respectively represented byformula I:

wherein the dotted lines represent continual crosslinked networks of—Si—O—.

In some embodiments, each of the silica materials 104 a and 104 b mayhave a particle size of 10 nm to 500 μm. However, the invention is notlimited thereto. In other embodiment, the size of the silica materials104 a and 104 b may be adjusted according to the needs.

It should be noticed that the quantum dots 102 a and 102 b arerespectively covered by the silica materials 104 a and 104 b, thus thethermal stability of the composite materials 100 a and 100 b areenhanced with respect to the conventional quantum dots without silicamaterial covering. In addition, since the projector color wheel of thepresent invention includes the composite material having quantum dots,the color gamut of the light produced by the projector color wheel ofthe present invention is enhanced compared with the color gamut usingconventional phosphors. Moreover, as shown in FIG. 2B, since the quantumdots 102 b are uniformly dispersed in the silica material 104 b withoutaggregation, the luminescence efficacy of the composite material 100 bis improved, which is suitable for surface package of photoelectricdevices, such as LED devices, and digital light processing (DLP)devices, such as DLP projector color wheels.

In some embodiments, each of the composite materials 100 a and 100 bfurther include a silicon resin (not shown) covering a surface of eachof the silica materials 104 a and 104 b. Hence, the thermal stabilitythe composite materials 100 a and 100 b are further enhanced and enablethe composite materials 100 a and 100 b to be easily moulded intovarious shapes and sizes depending on the application.

FIG. 3 is a flow-chat drawing illustrating a manufacturing flow of acomposite material according to a fourth embodiment of the invention.FIG. 4A and FIG. 4B are schematic drawings illustrating themanufacturing flow of the composite material according to FIG. 3.

Referring to FIG. 3, a method 300 for manufacturing the compositematerial of the fourth embodiment is as follows. First, a step 302 isperformed. A mixture is prepared. The mixture includes a plurality ofquantum dots and a non-polar solvent, wherein the quantum dots aredissolved in the non-polar solvent. In some embodiments, the mixture isstirred or sonicated at room temperature (e.g., 25° C.) to fullydissolve the quantum dots. The non-polar solvent may be but not limitedto cyclohexane, hexane, toluene, or a combination thereof. In someembodiments, a content of the quantum dots is 0.8-20 wt % and a contentof the non-polar solvent is 80-99.2 wt % based on the weight of themixture (i.e., a sum of the quantum dots and the non-polar solvent).

Next, steps 304 and 306 are performed. A polar solvent and a surfactantare prepared. In some embodiments, the polar solvent may be but notlimited to water. The surfactant may include organic compounds that areamphiphilic. That is, the organic compounds contain both hydrophobicgroups (e.g., tails) and hydrophilic groups (e.g., heads). Therefore,the surfactant contains both a polar-insoluble (e.g., water-insoluble)or non-polar-soluble (e.g., oil-soluble) component and a polar-soluble(e.g., water-soluble) component. For example, the surfactant willdiffuse in water and adsorb at the interface between oil and water, inthe case where water is mixed with oil. The water-insoluble hydrophobicgroup may extend out of the bulk water phase or into the oil phase,while the water-soluble head group remains in the water phase.

Incidentally, the order of the step 302, 304 and 306 can be adjustedaccording to the needs. That is, after preparing the mixture (i.e., thestep 302), the polar solvent and the surfactant are prepared (i.e., thesteps 304 and 306); however, the invention is not limited thereto. Inone embodiment, the steps 304 and 306 may be performed first, and thenthe step 302 is performed. In alternative embodiment, the steps 302, 304and 306 may be performed at the same time.

Step 308 is then performed. The mixture, the polar solvent and thesurfactant are mixed to form an emulsion. Referring to FIG. 4A, aftermixing the mixture, the polar solvent and the surfactant in a container203, an emulsion 201 is formed in the container 203. The emulsion 201may include a plurality of dispersed phases 206 and a continuous phase204. The dispersed phases 206 are dispersed in the continuous phase 204.As shown in the enlarged view of FIG. 4A, one of the dispersed phases206 and part of the continuous phase 204 constitute single micelle 205.A plurality of micelles 205 are dispersed uniformly in the emulsion 201.In addition, the micelle 205 also includes a plurality of surfactantcompounds 208. Each of the surfactant compounds 208 includes ahydrophilic group 208 a and a hydrophobic group 208 b. Since thedispersed phases 206 include the foregoing polar solvent, thehydrophilic groups 208 a face toward interfaces 210 between thedispersed phases 206 and the continuous phase 204. On the other hand,since the continuous phase 204 includes the foregoing non-polar solvent,the hydrophobic groups 208 b are away from the interfaces 210. As aresult, the surfactant compounds 208 are arranged as a spherical shape.Moreover, a plurality of quantum dots 202 are also included in theemulsion 201. The quantum dot surface changes from non-polar to polarwhen surrounded by surfactant molecules. During mixing the mixture, thequantum dots with polar surfaces tend to move from the less polarcontinuous phase 204 to the more polar dispersed phase 206 that issurrounded by the hydrophilic groups of the surfactants.

Referring back to FIG. 3 and FIG. 4B, a step 310 is then performed. Acatalyst and a silica precursor are added into the emulsion 201 to forma plurality of composite materials 200 in the dispersed phases 206respectively. Each of the composite materials 200 includes quantum dots202 and a silica material 212 (i.e., the silica precursor afterperforming the step 310). The quantum dots 202 are dispersed uniformlyin the silica material 212. In particular, steps of adding the catalystand the silica precursor may include a hydrolysis, a condensation and apolymerization. During the hydrolysis, the silica precursor is fullyhydrolyzed or partially hydrolyzed by H₂O from the foregoing polarsolvent, so as to form siloxane compounds with hydroxyl groups (OHgroups) attached on Si of the siloxane compounds. The hydrolysis scheme(1) is represented as below.

wherein each R is independently selected from the group consisting ofC₁₋₈ alkyl, cycloalkyl and aryl.

Then, during the condensation, two or more of the fully hydrolyzed orpartially hydrolyzed siloxane compounds are bonded together. Thecondensation scheme (2) or (3) is represented as below.

wherein each R is independently selected from the group consisting ofC1-8 alkyl, cycloalkyl and aryl.

During the polymerization, one hydrolysis and one condensation arerepeated one or more times to form the foregoing silica materials.

In some embodiment, the catalyst may be a base. The base may be but notlimited to ammonia, ammonium fluoride, sodium hydroxide or a combinationthereof. The silica precursor may include tetramethyl orthosilicate(TMOS), tetraethyl orthosilicate (TEOS), or a combination thereof. Thecatalyst are polar molecules situated in the polar dispersed phase 206,which is generally separated from the non-polar silica precursor in thenon-polar continuous phase 204. During mixing, silica precursor andcatalyst will come into contact at the polar and non-polar interface dueto the random movements of the molecules and initiate the polymerizationreaction. Thus the silica materials 212 tend to surround the quantumdots 202 in the polar dispersed phase 206, forming the foregoingcomposite materials 200. It should be noted that a number of the quantumdots 202 in each of the silica materials can be controlled by the weightratio of the quantum dots 202 and the silica precursor. In addition, theparticle size of each of the composite materials 200 can also becontrolled by the size of each of the micelles 205. That is, thecomposite materials 200 having similar or the same particle size can beobtained according to the foregoing method of the present invention.Each of the composite materials 200 may have similar or the same numberof the quantum dots 202 therein. In some embodiments, the weight ratioof the quantum dots 202 to the silica precursor ranges from 1:1 to1:200.

After performing the step 310, a step 312 is performed. A centrifugationprocess and at least one cleaning process are performed to collect theprecipitate of the composite materials 200. In some embodiments, thecleaning process may include using ethanol to wash resulting productsafter performing the centrifugation process.

In one embodiment, the composite materials 200 may be mixed withsilicone and disposed onto a LED chip. The silicone may be acommercially available silicone (e.g., Dow Corning® OE-6370). Morespecifically, the LED chip is one component of a LED device. The LEDdevice may include a substrate with a cavity and the LED chip disposedin the cavity of the substrate. The composite material formed fromforegoing method 300 is mixed with silicone and filled in the cavity ofthe substrate and covers a surface of the LED chip. The compositematerial includes a plurality of quantum dots. The quantum dots may emitred, green, blue or any other colored lights desired. The quantum dotsare able to absorb light energy emitted from the LED chip and re-emitthe absorbed energy as light of a different wavelength. The quantum dotsmay have variously-regulated light emitting wavelengths. For example,one white LED device may be fabricated by combining red and greenquantum dots with a blue LED chip. Alternatively, another white LEDdevice may be fabricated by combining red, green, and blue quantum dotswith a short visible (Vis) or an ultraviolet (UV) LED chip.

It should be noted that the silica material used in the LED device maybe a modification-free silica material. Specifically, themodification-free silica material is able to react with the siliconewithout any additional functional groups, such as methacrylate, vinyl,vinyl acetate, alkene, thiol, or a combination thereof. If the silicamaterial is modified with an additional functional group,propylmethacrylate (as in TMOPMA) for example, the thermal stability ofthe composite material formed is decrease (see FIG. 10). That is, thecomposite material having the modified silica material is not suitablefor surface package of the light emitting apparatus, such as the LEDdevice. On the other hand, the composite material of the embodimenthaving the modification-free silica material, thus the thermal stabilityof the composite material formed is enhanced (see FIG. 10).

In alternative embodiment, the composite materials 200 may be used ascolor converters of a projector color wheel. Since the quantum dots 202are encapsulated by the silica material 212, the thermal endurance ofthe composite material 200 are enhanced. Therefore, the color gamut of aprojector is not only improved, the luminance property of the quantumdots 202 disposed in the projector color wheel of the projector is alsomaintained.

In addition, the composite materials 200 may be mixed with luminescentphosphor material, so as to supplement the deficiency of the luminescentphosphor material and thus increase the color gamut of the lightemitting apparatus, such as the projector color wheel or the LED device.In detail, a mixture includes the luminescent phosphor material and thecomposite material. The luminescent phosphor material is capable ofemitting light with a first color. The composite material includes aplurality of quantum dots capable of emitting light with a second colorand a silica material encapsulating surfaces of the quantum dots. Thefirst color and the second color are complementary to each other.

In one embodiment, the luminescent phosphor material may be ayellow-emitting or green-emitting phosphor material with dominantemission wavelength of 500 nm to 600 nm, such as yttrium aluminiumgarnet (YAG; Y₃Al₅O₁₂:Ce³⁺), silicate ((Ba, Sr)₂SiO₄:Eu²⁺), β-SiAlON(Si_(6-z)Al_(z)O_(z)N_(8-z):Eu²⁺), or γ-AlON(Al_(1.7)O_(2.1)N_(0.3):Mn²⁺, Eu²⁺). Due to its deficiency in emittingred color, a red-emitting quantum dot encapsulated in silica material(dominant emission wavelength of 600 nm to 650 nm) may be used tosupplement this deficiency and thus increase the color gamut of thefinal luminescent composite material. For example, when the luminescentphosphor material is a yellow-emitting phosphor, and the quantum dotsmay be red quantum dots, green quantum dots or a combination thereof. Insome embodiments, when the luminescent phosphor material is agreen-emitting phosphor, and the quantum dots may be red quantum dots.In alternative embodiments, the luminescent phosphor material may be ared-emitting phosphor material with dominant emission wavelength of 590nm to 680 nm, such as CaAlSiN₃:Eu²⁺ or KSF (K₂SiF₆:Mn⁴⁺). Due to itsdeficiency in emitting green color, a green-emitting quantum dotencapsulated in silica material (dominant emission wavelength of 500 nmto 550 nm) may be used to supplement this deficiency and thus increasethe color gamut of the final luminescent composite material.

FIG. 11 is a schematic drawing illustrating an optical film according toan embodiment of the invention.

Furthermore, the composite materials 200 may exist in the form of afilm. Specifically, as shown in FIG. 11, an optical film 400 includes afirst component 402, a second component 408 and a third component 410.The first component 402 includes one or more quantum dots 404 and asilica material 406 encapsulating surfaces of the one or more quantumdots 404. The second component 408 includes a UV curable compositematerial. The third component 410 includes two PET (polyethyleneterephthalate) substrate sheets 410 a and 410 b that sandwich the firstcomponent 402 and the second component 408 in between. The firstcomponent 402 is dispersed in the second component 408. In someembodiments, the UV curable composite material may include 2-phenylethylmethacrylate, triaryl isocyanurate (TAIC), diallyl phthalate, and aphotoinitiator. In addition, the one or more quantum dots 404 areencapsulated by the silica material 406, thus, the silica material 406is able to prevent oxygen and water vapor from contacting the dispersedquantum dots 404. Compared with organic material, such as polymer orresin, the silica material 406 has a better effect of preventing oxygenand water vapor. Therefore, the optical film 400 is able to be directlyused in a light emitting apparatus without using expensive gas barrierlayers on the third component (PET sheets) 410 to protect the opticalfilm 400.

In order to improve reliability of the invention, the following listsseveral examples and several comparative examples to illustrate thecomposite material of the invention further. Although the followingexperiments are described, the material used and the amount and ratio ofeach thereof, as well as handling details and handling procedures, etc.,can be suitably modified without exceeding the scope of the invention.Accordingly, restrictive interpretation should not be made to theinvention based on the embodiments described below.

Experimental Example 1

CdSe/ZnS quantum dots (200 mg; prepared according to literatureprocedures) are dissolved in 50 ml of cyclohexane to form a mixture.Igepal CO-520 (purchased from Sigma-Aldrich) is added in the mixture,wherein a weight ratio of quantum dot to Igepal CO-520 is 1:5. Water (50ml) is added and stirred at room temperature (about 25° C.) until halfof the liquid evaporated. Ammonia (384 μl) and ethyl acetate (2 ml) isthen added and mixed homogenously before 320 μl of tetraethylorthosilicate (TEOS) is added and reacted for 8 hours. After thereaction, the precipitate is collected by centrifugation and then washedwith ethanol three to five times. The precipitate is dried in the ovenat 70° C. for one hour to form a composite material of Experimentalexample 1. The composite material of Experimental example 1 ischaracterized by transmission electron microscopy (TEM). As shown inFIG. 5, the CdSe/ZnS quantum dots are encapsulated by the silica.

Experimental Example 2

In the following, the manufacturing method of composite materials ofExperimental example 2 to Experimental example 4 are conducted insimilar methods described as Experimental example 1.

The composite material of Experimental example 2 includes green CdSe/ZnSquantum dots and silica (SiO₂), wherein the green CdSe/ZnS quantum dotsare encapsulated by silica. Then, 5 wt % of composite material ofExperimental example 2 and 95 wt % of two-part silicone (Dow Corning®OE-6370) are mixed, then applied onto a section of a digital lightprocessing (DLP) projector color wheel and cured at 100° C. for 3 hours.The projector color wheel was then installed into a DLP projector toproduce green test screen. As shown in FIG. 6A, a green test screen wasproduced successfully using silica encapsulated green quantum dots,showing that the silica encapsulation allowed the green quantum dots tosurvive the extreme environment (e.g., high temperature up to 180° C.)inside the projector.

Experimental Example 3

The composite material of Experimental example 3 includes red CdSe/ZnSquantum dots and silica (SiO₂), wherein the red CdSe/ZnS quantum dotsare encapsulated by silica. Then, 5 wt % of composite material ofExperimental example 3 and 95 wt % of two-part silicone (Dow Corning®OE-6370) are mixed, then applied onto a section of a digital lightprocessing (DLP) projector color wheel and cured at 100° C. for 3 hours.The projector color wheel was then installed into a DLP projector toproduce red test screen. As shown in FIG. 6B, a red test screen wasproduced successfully using silica encapsulated red quantum dots,showing that the silica encapsulation also allowed the red quantum dotsto survive the extreme environment (e.g., high temperature up to 180°C.) inside the projector.

Experimental Example 4

4 wt % of green CdSe/ZnS quantum dots encapsulated by silica, 1 wt % ofred CdSe/ZnS quantum dots encapsulated by silica and 95 wt % of two-partsilicone (Dow Corning® OE-6370) are mixed to form a mixture. The mixtureis dispensed onto a blue LED chip (i.e., an emission wavelength thereofis 440˜460 nm) and cured at 100° C. for 3 hours. The LED output spectrumis shown in FIG. 7. As shown in FIG. 7, the silica encapsulated quantumdots are able to convert the source blue light from the LED chip togreen and red lights.

Comparative Example 1

Reverse Emulsion Synthesis of Silica Beads Embedded with Quantum Dots

A solution of CdSe/ZnS core/shell quantum dots (containing 70 mg ofinorganic material) was subjected to evaporation to remove most of thesolvent, which in this case was toluene, and then mixed with silanemonomers (e.g., 0.1 mL of 3-(trimethoxysilyl)propylmethacrylate (TMOPMA)and 0.5 mL of tetramethoxy silane (TEOS)) until a clear solution wasobtained.

10 mL of degassed cyclohexane/Igepal™ CO-520 (CO-520 isC₉H₁₉-Ph-(OCH₂CH₂)_(n)—OH where n=5) (18 mL/1.35 g) was prepared in a 50mL flask and 0.1 mL of 4% NH₄OH injected to form a stable reverseemulsion. The Cyclohexane/CO-520/NH₄OH mixture was then mixed with thequantum dots/silane monomers mixture and stirred at 500 rpm under N₂overnight. Modified silica beads containing quantum dots were recoveredby centrifugation and washed with cyclohexane twice. The resultingsediment was then dried under vacuum.

Experimental Example 5

CdSe/ZnS quantum dots (200 mg; prepared according to literatureprocedures) are dissolved in 50 ml of cyclohexane to form a mixture.Igepal CO-520 (purchased from Sigma-Aldrich) is added in the mixture,wherein a weight ratio of quantum dot to Igepal CO-520 is 1:5. Water (50ml) is added and stirred at room temperature (about 25° C.) until halfof the liquid evaporated. Ammonia (384 μl) and ethyl acetate (2 ml) isthen added and mixed homogenously before 210 μl of tetramethylorthosilicate (TMOS) is added and reacted for 8 hours. After thereaction, the precipitate is collected by centrifugation and then washedwith ethanol three to five times. The precipitate is dried in the ovenat 70° C. for one hour to form a composite material of Experimentalexample 5.

LED Lifetime Test

Quantum dots encapsulated by modification-free silica were synthesizedaccording to Experimental example 5 and were mixed with a two-partsilicone (Dow Corning® OE-6370). The mixture was dispensed onto a blueLED chip (i.e., an emission wavelength thereof is 440˜460 nm) and curedat 100° C. for 3 hours. The fabricated LEDs were tested and continuouslypowered with a forward current of 20 mA. The LED efficacy (e.g., bluelight from the LED plus green and red lights emitted by quantum dots) inlumen and quantum dots photoluminescence (PL) intensity (e.g., green andred lights emitted by quantum dots only) was measured periodically usinga photometric integrating sphere (diameter=10 cm) with a spectral lightmeter (OPTIMUM SRI-2000).

Similarly, quantum dot-containing silica microbeads prepared asComparative example 1 can be mixed with an LED encapsulant (e.g., ShinEtsu SCR1011 or Shin Etsu SCR1016) using sufficient stirring to ensuregood dispersion within the encapsulating polymer. The encapsulantmixture was dispensed then onto a blue LED chip (i.e., an emissionwavelength thereof is 440˜460 nm) and cured under an inert atmosphereusing standard conditions for the LED encapsulant used. The fabricatedLEDs were tested and continuously powered with a forward current of 20mA. The LED efficacy (e.g., blue light from the LED plus green and redlights emitted by quantum dots) in lumen and quantum dotsphotoluminescence (PL) intensity (e.g., green and red lights emitted byquantum dots only) was measured periodically using a photometricintegrating sphere (diameter=10 cm) with a spectral light meter (OPTIMUMSRI-2000).

FIG. 10 is a plot of LED efficacy and quantum dot photoluminescence (PL)intensity of LED with modification-free silica encapsulated quantum dots(Experimental examples 5) or LED with modified silica encapsulatedquantum dots (Comparative example 1). As can be seen in FIG. 10, theefficacy of LED with modification-free silica encapsulated quantum dotsdoes not exhibit a sharp initial decrease as shown by LED with modifiedsilica encapsulated quantum dots. Furthermore, LED withmodification-free silica encapsulated quantum dots exhibited lessdecrease in efficacy and photoluminescence (PL) throughout the wholetest period. This clearly illustrated that quantum dots encapsulated bymodification-free silica material (Experimental examples 5) are morestable than quantum dots encapsulated by modified silica material(Comparative example 1).

Experimental Example 7

Color Wheel Application

Red CdSe/ZnS QDs encased in silica (10 wt %) and yellow yttriumaluminium garnet (YAG) phosphor (40 wt %) mixed with two-part silicone(Dow Corning® OE-6370; 50 wt %) was applied on a section of the colorwheel and cured at 100° C. for 3 hours. The color wheel was theninstalled into a DLP projector. The silica encapsulated red quantum dotsare able to supplement the deficiency of red color from YAG phosphor,and improve the color gamut of the projector.

Experimental Example 8

LED Application

Silica encapsulated red quantum dots (3 wt %), yellow yttrium aluminiumgarnet (YAG) phosphor (5 wt %), and silicone (Dow Corning® OE-6370; 92wt %) are mixed to form a mixture. The mixture is dispensed onto a blueLED chip (i.e., an emission wavelength thereof is 440˜460 nm) and curedat 100° C. for 3 hours. The LED output spectrum is shown in FIG. 8. Asshown in FIG. 8, the silica encapsulated red quantum dots are able tosupplement the deficiency of red color from YAG phosphor (see the dottedline in FIG. 8), leading to an improved color gamut.

Experimental Example 9

Silica encapsulated red quantum dots (3 wt %) and green quantum dots (10wt %) are mixed with a UV curable composite material comprisingAG-F-26729 (48 wt %; Angene), TAIC™ (24 wt %; Nippon Kasei Chemical),DAISO DAP™ (14 wt %; Osaka Soda) and Darocur® TPO (1 wt %; CibaSpecialty Chemicals Inc.). The mixture (100 μm thick) is sandwichedbetween two polyethylene terephthalate (PET) sheets (100 μm thick each)and exposed to UV light (370 nm, 400 W, 2 minutes) to form an opticalthin film. The optical thin film was installed into a 7-inch blue (445nm) backlight unit and stored at 85° C. with the light power constantlyswitched on (2.4 mW/cm²) for 1000 hours. The luminescence intensity testof the backlight unit is measured with a Konica Minolta CS-100 meter atdifferent time interval.

As shown in FIG. 9, the luminescence intensity of the backlight unitremained constant throughout the test. This clearly illustrated thatthere was no decay in the photoluminescence of the optical film insidethe backlight unit.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. An optical film comprising: a first componentcomprising a plurality of quantum dots; and a silica materialencapsulating surfaces of the quantum dots, wherein the quantum dots aredispersed uniformly in the silica material; a second componentcomprising a UV curable composite material, wherein the first componentis dispersed in the second component; and a third component comprisingtwo PET (polyethylene terephthalate) substrate sheets, wherein the firstcomponent and the second component are disposed between the two PETsubstrate sheets.
 2. The optical film according to claim 1, wherein thesilica material comprises an inorganic polymer made from tetramethylorthosilicate (TMOS) or tetraethyl orthosilicate (TEOS).
 3. The opticalfilm according to claim 1, wherein the UV curable composite materialcomprises 2-phenylethyl methacrylate, triaryl isocyanurate (TAIC),diallyl phthalate, and a photoinitiator.
 4. The optical film accordingto claim 1, wherein the optical film is used in a light emittingapparatus, and the light emitting apparatus comprises a backlight unitin a flat-panel display apparatus, a liquid crystal display monitor or acombination thereof.